Various types of internal combustion engines for vehicles may burn gaseous fuels in place of, or in combination with, conventional liquid fuels like gasoline. Gaseous fuels may include hydrogen, natural gas, propane, and lighter flammable hydrocarbon derivatives, for example. Gaseous fuels may provide various advantages relative to conventional liquid fuel injection, such as reduction of nitrogen oxide emissions, particulate matter, and hydrocarbons, lower fuel cost, and/or the ability to utilize fuels other than fossil fuels to power the vehicle.
Gaseous fuels are generally stored on-board the vehicle in supercooled liquefied form or in one or more pressurized tanks, which present various challenges that are not encountered using conventional liquid fuels. Fuel cost and storage are both affected proportionately with fuel consumption. Even though standard hydrogen engines are among the most efficient automotive engines known, the disadvantage relative to fuel storage and cost remain barriers to widespread marketability. As such, fuel efficiency remains a primary concern for automotive OEMs attempting to introduce low-cost hydrogen and other gaseous fuel products. The present disclosure recognizes that fuel concentration and distribution should be carefully considered to balance the tradeoff between NOx emissions, heat transfer to the cylinder walls of the engine, and overall efficiency of the engine.